The Role of Ferric Oxide Nanoparticles in Improving Lubricity and Tribo-Electrochemical Performance During Chemical–Mechanical Polishing

The role of ferric oxide nanoparticles on the lubricating characteristics of passivating films formed on stainless steel (SS) was discussed in this study. The tribo-electrochemical behavior of mirror-like polished AISI 304 SS, used as an exemplary material, was evaluated in various electrolytes by means of a simulated chemical–mechanical polishing process in laboratory scale. It was clearly demonstrated that a suitable combination of abrasives (ferric oxide nanoparticles) and an oxidizer (nitric acid) can act as an effective lubricant that lowers the friction and wear of the AISI 304 SS surfaces. The excellent lubricating and anti-corrosion properties shown by a slurry containing a high content of ferric oxide nanoparticles at high nitric acid concentrations were attributed to the formation of a stable and robust passive film that was composed of chromium oxide and a mixture of iron oxides. The lack of ferric oxide nanoparticles in two solutions containing nitric acid of different concentrations led to pitting corrosion and abrasive wear. When low concentrations of both ferric oxide nanoparticles and nitric acid were used, wear-accelerated corrosion became the dominant mechanism that was caused by the presence of third-body wear particles in the contact zone.     

A micro-contact and wear model for chemical–mechanical polishing of silicon wafers

A micro-contact and wear model for chemical–mechanical polishing (CMP) of silicon wafers is presented in this paper. The model is developed on the basis of elastic–plastic micro-contact mechanics and abrasive wear theory. The synergetic effects of mechanical and chemical actions are formulated into the model. A close-form equation of material removal rate from the wafer surface is derived relating to the material, geometric, chemical and operating parameters in a CMP process. The model is evaluated by comparing the theoretical removal rates with those experimentally determined. Good agreement is obtained for both chemically active and inactive polishing processes. The model reveals some insights into the micro-contact and wear mechanisms of the CMP process. It suggests that the removal rate is sensitive to the particle concentration in the slurry, more sensitive to the applied load and operating speed and most sensitive to the surface hardness and slurry particle size. The model may be used to study the effects of different materials, geometry, slurry chemistry and operating conditions on CMP processes.     

ULSI制造中铜化学机械抛光的腐蚀磨损机理分析

以超大规模集成电路(ULSI)芯片多层互连结构制造中的关键平坦化工艺——铜化学机械抛光(Cu—CMP)为研究对象，针对Cu—CMP中存在的抛光液的化学腐蚀作用和磨料的机械磨损现象，采用腐蚀磨损理论分析了Cu—CMP材料去除机理。提出铜CMP的材料去除中存在着机械增强的化学腐蚀和化学增强的机械磨损，并分析了Cu—CMP的静态腐蚀材料去除、机械增强的腐蚀去除与化学增强的机械去除机理。     

A review on the progress towards improvement in surface integrity of Inconel 718 under high pressure and flood cooling conditions

Self-conditioning performance of polishing pad is an important characteristic to influence processing efficiency and service life in chemical mechanical polishing (CMP). The slurry can react with the pad surface, which affects its self-conditioning performance in fixed abrasive polishing process. Wear ratio of wafer material removal rate (MRR) and pad wear rate is introduced to evaluate self-conditioning performance of fixed abrasive pad (FAP). To clear the effect of chemical additive on FAP self-conditioning, wear ratio, FAP surface topography, friction coefficient, and acoustic emission signal of polishing process were investigated in fixed abrasive polishing of quartz glass with ferric nitrate, ethylenediamine (EDA), and triethanolamine (TEA) slurry, respectively. Results indicate that TEA slurry can provide excellent self-conditioning of FAP in fixed abrasive polishing of quartz glass. MRR and wear ratio maintain high levels during the whole polishing process. Friction coefficient and acoustic emission signal are more stable than that of the other two chemical additives. An appropriate amount of TEA, which is beneficial to enhance MRR and extends service life of FAP, is added in the polishing slurry to improve FAP self-conditioning in fixed abrasive polishing process.     

Investigation of Chemical/Mechanical Polishing of Niobium

A chemical/mechanical method for polishing flat niobium sheets to a mirror finish was developed. Various polishing slurries with different open circuit potentials and pH values were considered. All slurries fell within the niobate region of the Pourbaix diagrams, indicating that slurries are in a thermodynamically stable region. Oxidation characteristics of the niobium in the various slurries were determined by XPS and confirmed previously published work that niobium forms various layers of stable niobium oxides roughly 4.5–4.7 nm in thickness on the surface. A multi-step polishing method that relies on mechanical abrasion of the surface proved to be effective, and particles of different hardness and size were explored. Niobium wafers with initial peak-to-valley (PV) surface roughness of 3 to 7 μm were polished. The multi-step process utilized a slurry containing 1 μm diameter alumina particles to polish this initial roughness down to a submicrometer level. The final polish was provided by a slurry containing smaller particles. The oxide slurry with 70 to 100 nm silica particles gave the best mirror finished surface, with PV = 235 nm, Ra = 32 nm, and RMS = 39 nm. While polishing caused some disorder in the niobium metal, using the oxide slurry gave results closer to those obtained by buffered chemical polish (BCP), which exhibits the highest degree of atomic order based on XPS studies. A polishing process starting with mechanical abrasion, followed by a two-step mechanical polish, is successful for obtaining smooth niobium surfaces on flat wafers.     

PERFORMANCE CHARACTERIZATION OF CERIUM OXIDE ABRASIVES FOR CHEMICAL-MECHANICAL POLISHING OF GLASS

Investigation of the nature of chemomechanical polishing (CMP) for glass requires an in-depth knowledge of the influences of abrasive physical properties and slurry chemistry. In the present work, eight cerium oxide abrasives were used to polish fused silica on a polyurethane pad. Results from pre-polished surfaces re-polished in aqueous and non-aqueous suspensions and from corrosion testing of solutions recovered from abrasive suspensions were used to discern chemical, chemomechanical, and mechanical equivalents for each abrasive. Performance indices (i.eabrasive quality values) were generated from the equivalents and related to conventional polishing of lapped surfaces. Optimally performing abrasives were found to require a balance of equivalents (i.eset ratio) as dictated by inherent chemical activities, heat treatments, and milling. From solution chemistry testing, particle/workpiece attraction via surface charge was found to increase the chemomechanical effect. The CMP mechanism is concluded to be a chemical reaction at the particle/workpiece interface promoted primarily by mechanical interactions such as abrasion, with both cerium oxide and rare-earth oxyfluoride constituents promoting the reaction.     

Material Removal Mechanism of Copper CMP from a Chemical�CMechanical Synergy Perspective

The material removal in chemical?Cmechanical planarization/polishing (CMP) of copper involves both chemical and mechanical effects. The roles of chemical corrosion, abrasive wear, and their synergistic effects on the material removal mechanism were studied by electrochemical analysis and nano-scratching method using atom force microscopy, respectively. Combining with the results of CMP experiments, dominant factors (chemistry and mechanics) in slurries within the range of pH 3.0?C10.0 were assessed. Consequently, a removal mechanism map of copper CMP depending on pH values was constructed. In the alkaline slurry, the wear?Ccorrosion effect predominated in the material removal at pH 8.0 and 9.0; while the copper removal mechanism changed to corrosion?Cwear action in the acidic slurry from pH 4.0 to 6.0, and good surface quality was also obtained. The results and the strategies provide thorough understanding of the material removal mechanism and further optimization of the CMP process.     

Effects of particle size, polishing pad and contact pressure in free abrasive polishing

The objective of this research is to better understand the mechanisms of material removal in the free abrasive polishing process. Experiments were carried out to understand the effects of particle size, polishing pad and nominal contact pressure on the wear rate and surface roughness of the polished surface. A theoretical model was developed to predict the relationship between the polishing parameters and the wear rate for the case of hard abrasive particles sandwiched between a soft pad and a workpiece (softer than the abrasive particles). Experimental results and theoretical predictions indicate that the wear rate increases with an increase in particle size, hardness of polishing pad and nominal contact pressure, and with a decrease in elastic modulus of the polishing pad. Surface roughness increases with an increase in particle size and hardness of polishing pad, and nominal contact pressure has little effect on the roughness. A dimensionless parameter, wear index which combines all of the preceding parameters, was introduced to give a semi-quantitative prediction for the wear rate in free abrasive polishing. It is also suggested that when polishing hard material, in order to achieve a high materials removal rate and a smooth surface, it is preferable to use diamond as the polishing particles because of their high deformation resistance.     

CMP behavior of alumina/metatitanic acid core–shell abrasives on sapphire substrates

The abrasive is one of the important influencing factors during the chemical mechanical polishing (CMP) process. Although α-alumina is one of the most commonly used sapphire polishing abrasives due to its high hardness, it often results in surface damage. To receive lower surface roughness and high material removal rate, a common approach is to modify the surface of alumina. In this work, a series of alumina/metatitanic acid composite abrasives with core–shell structure were synthesized. The CMP performances of the pure alumina and alumina/metatitanic acid core–shell abrasives on sapphire substrates were investigated after polishing under the same conditions. Experimental results indicate that the alumina/metatitanic acid core–shell abrasives can not only improve the surface quality, but also further enhance the material removal rate. Furthermore, through the X-ray photoelectron spectroscopy test, this study investigated the chemical effect mechanism of the alumina/metatitanic acid core–shell abrasives in sapphire CMP. The results show that solid-state chemical reactions occur between metatitanic acid shell and sapphire surface during CMP process. We also investigated the mechanical friction mechanism through abrasive wear and adhesive wear.     

低速冲击下的界面响应和磨损行为*

为探究低速冲击下界面响应与磨损行为之间的联系，开展多周次的低速冲击磨损实验；通过分析冲击过程中的接触力峰值、接触时长、接触力冲量、动能耗散等，研究冲击速度对接触界面的力学响应的影响；通过对冲击磨痕的磨损轮廓和形貌、磨损体积的检测分析，以及对磨痕区域元素组分变化的测试，研究冲击速度对接触界面磨损损伤行为的影响。结果表明：冲击速度的增加会导致接触界面在更短的时间内受到更强烈的力学作用；能量吸收率对冲击速度的变化不敏感，但冲击速度的提高会导致单位能量造成的磨损损伤逐渐降低；冲击磨痕可分为以塑性变形和以剥层磨损为主要损伤形式的2种区域；磨损区内经历了严重的摩擦氧化，并随着冲击速度的增加发生冲击副材料转移。因此，冲击速度越高，接触界面间的摩擦越剧烈，形成的表面氧化层避免了冲击副与基底材料的直接接触，延缓了磨损损伤的进一步发展。     

Analysis of Feature-Scale Wear in Chemical Mechanical Polishing: Modeling and Experiments

An asperity-scale wear model was developed to predict feature-scale wear in chemical–mechanical polishing (CMP), and was compared to the measured evolution of a lithographically patterned feature during full-scale CMP tests. To conduct this study, a lithographic technique was used to pattern a set of raised square features into a Cu-coated silicon wafer. Two-dimensional contact profilometry was used to measure the topography of an isolated feature on each wafer both before polishing and at various intervals throughout the polishing process. In the wear modeling formulation, a pad deflection-based contact mechanics model was developed and combined with a particle-based wear model to predict the wear evolution of the sample during CMP. The predicted wear of the sample feature was found to agree well to experimental results.     

铜抛光液中缓蚀剂5-氨基四唑(ATA)的作用机制研究

采用静态腐蚀实验、接触角测试、XPS等手段,比较在不同pH值下抛光液中缓蚀剂(5-氨基四唑(ATA),苯并三唑(BTA))对铜表面化学机械抛光(CMP)的影响,并探讨ATA在铜表面的作用机制。结果表明,BTA和ATA是优良的铜缓蚀剂,当pH值为3～10时,两者可在铜表面成膜,保护铜表面不受腐蚀,从而降低铜片的静态腐蚀速率和去除率,其中当pH=4时,2种缓蚀剂表现出最佳的缓蚀性能。当pH值为3～5时,ATA的缓蚀性能优于BTA。ATA通过四唑环上的N原子和氨基上的N原子吸附在铜表面,形成保护膜,从而抑制了H2O2对铜表面的腐蚀,改善了表面质量,是一种优良的适用于酸性铜抛光液的缓蚀剂。     

氧化剂含量对304不锈钢化学机械抛光的影响

为了探究氧化剂含量对304不锈钢化学机械抛光的影响及其作用机制,采用过氧化氢作为氧化剂,研究不同氧化剂质量分数下304不锈钢材料去除率及表面粗糙度值的变化规律,并基于接触角和电化学试验分析过氧化氢在抛光过程中的作用机制。结果表明：化学机械抛光过程中过氧化氢含量的增加有利于304不锈钢表面氧化膜的生成,从而有效提高304不锈钢的材料去除率及表面质量;但是过高的过氧化氢含量会导致304不锈钢表面氧化膜致密,使得化学作用与机械作用失衡从而造成304不锈钢表面质量下降;当过氧化氢质量分数为0.04%时,抛光后304不锈钢表面粗糙度值最低,仅有2.5 nm,材料去除率达到324.21 nm/min。     

研磨抛光表面微孔织构的形成

由于表面织构可以改善机械零部件的摩擦磨损特性,延长其使用寿命,本文基于研磨抛光方法开发了一种表面微孔快速成型技术。该技术的特点是微孔成型过程与抛光过程同步进行。选取载荷为0.023 2 MPa、研磨液浓度为9%、研磨速度为2.09m/s以及研磨粒径为0.5μm作为考察条件,研究了微孔在金属表面的形成机理,证明了表面微孔是由于研磨颗粒在表面预制微缺陷处做涡旋运动,同时工件的自转使研磨颗粒在360°方向上依次磨削微缺陷壁面而形成的。利用该技术所形成的微孔周边为圆弧过度,无其他织构技术所形成的凸起和毛刺,因此无需进行抛光后处理。利用该方法在一定的织构条件下可以形成次生孔,从而进一步增加工件的比表面积。另外,选取合适的研磨时间在适当的织构条件还可以在工件表面形成微米及亚微米孔,为减少类金刚石(DLC)薄膜内应力和提高界面结合强度提供了新的思路。研究显示研磨抛光表面微孔织构技术具有设备简单、效率高、适合大面积,多种材料织构等特点。     

超声波精细雾化抛光石英玻璃的抛光液研制*

为了配制适用于JGS1光学石英玻璃超声波精细雾化抛光的特种抛光液,以材料去除率和表面粗糙度为评价指标,设计正交试验探究抛光液中各组分含量对雾化抛光效果的影响,并对材料去除机制进行简要分析。结果表明：各因素对材料去除率的影响程度由大到小分别为SiO2、pH值、络合剂、助溶剂和表面活性剂,对表面粗糙度影响程度的顺序为SiO2、表面活性剂、pH值、助溶剂和络合剂;当磨料SiO2质量分数为19%,络合剂柠檬酸质量分数为1.4%,助溶剂碳酸胍质量分数为0.2%,表面活性剂聚乙烯吡咯烷酮质量分数为0.9%,pH值为11时,雾化抛光效果最好,材料去除率为169.5 nm/min,表面粗糙度为0.73 nm;去除过程中石英玻璃在碱性环境下与抛光液发生化学反应,生成低于本体硬度的软质层,易于通过磨粒机械作用去除。使用该抛光液进行传统化学机械抛光和雾化化学机械抛光,比较两者的抛光效果。结果表明：两者抛光效果接近,但超声雾化方式抛光液用量少,仅为传统抛光方式的1/7。     

曲轴连杆颈砂带抛光运动模型的研究

砂带研抛是一种很好的机械加工工艺,它在提高零件的表面光洁度,增强零件的耐磨性和疲劳寿命方面应用广泛。对砂带研抛曲轴连杆颈机构做了详细地分析,并讨论了不同抛光块以及不同接触方式对抛光质量的影响,同时还分析了随动误差对抛光质量的影响。     

Chemistry enhanced shear thickening polishing of Ti–6Al–4V

To obtain the great surface quality of Ti–6Al–4V and achieve high efficiency in the polishing process, the chemistry enhanced shear thickening polishing (C-STP) was proposed, and the polishing performance of different pH slurry was studied. The results show that the material removal rate gradually increases as the pH value decreases from 10 to 1, and the best surface quality is obtained at pH 2. The corrosion current density and potential were measured by potentiodynamic polarization under three typical pH values. It is confirmed that the most massive corrosion rate presents at pH 2, and the passive film is most susceptible to be produced at pH 10. The reaction resistance was measured by electrochemical impedance spectroscopy to clarify the polishing mechanism. Under acidic conditions, the chemical reaction product on the surface can be quickly removed by mechanical action of the abrasive. On the contrary, the passive film formed on the surface under the alkaline condition is difficult to be removed. The corrosion reaction products were determined by X-ray photoelectron, and the chemical reaction under acid-base environment was derived. MRR reached 107.3 nm/min under the selected process parameters, and the surface roughness (S_a) is reduced from 124 nm to 8.6 nm within 15 min.     

Micro- and Nano-scale Tribo-Corrosion of Cast CoCrMo

Previous studies have established that some of the wear damage seen on cast CoCrMo joint surface is caused by entrained third-body hard particles. In this study, wet-cell micro-indentation and nano-scratch tests have been carried out with the direct aim of simulating wear damage induced by single abrasive particles entrained between the surfaces of cast CoCrMo hip implants. In situ electrochemical current noise measurements were uniquely performed to detect and study the wear-induced corrosion as well as the repassivation kinetics under the micro-/nano-scale tribological process. A mathematical model has been explored for the CoCrMo repassivation kinetics after surface oxide film rupture. Greater insights into the nature of the CoCrMo micro-/nano-scale wear-corrosion mechanisms and deformation processes are determined, including the identification of slip band formation, matrix/carbide deformation, nanocrystalline structure formation and strain-induced phase transformation. The electrochemical current noise provides evidence of instantaneous transient corrosion activity at the wearing surface resulting from partial oxide rupturing and stripping, concurrent with the indent/scratch.     

A disc-on-flat wear test under starved lubrication

The ‘disc-on-flat’ system has been used for testing wear under starved lubrication conditions. The rotating discs were made of a carbon steel, the surface finish of the discs being ground. Some of the discs were treated by ‘vibrogrooving’, to form regular microrelief. The flat counterface was made of a ground copper alloy. An industrial oil was used as a lubricant in a one-drop test procedure. Microreliefs of a non-touching design with a relative groove area of 34% caused less wear than microreliefs of a touching type with a relative groove area of 50%, whereas the wear caused by the ground disc was high, with seizure after 200–250 m of sliding distance. A one-drop disc-on-cylinder test also showed that the wear caused by discs with regular microrelief was considerably less than that caused by discs treated by conventional finishing (grinding, polishing).     

Experimental investigation of process parameters for roll-type linear chemical mechanical polishing (Roll-CMP) system

The fabrication processes for electronic components are now demanding a higher degree of planarity for integration and multistacking, with chemical mechanical polishing (CMP) processes replacing conventional etching or mechanical polishing owing to their ability to attain global planarization. As CMP has been applied to more and more fields, new types of CMP machines have been developed. This study introduces a novel roll-type linear CMP (Roll-CMP) process that uses a line-contact material removal mechanism to for the polish flexible substrates, and examines the effect of the process parameters on the material removal rate (MRR) and its nonuniformity (NU). The parameters affecting the Roll-CMP process include down force, roll speed, table feed rate, slurry flow rate, slurry temperature, and the table oscillation length. Increasing the down force, roll speed, slurry flow rate, and slurry temperature resulted in a high average MRR (MRR_avg). Further, the MRR_avg was found to decrease with an increase in the oscillation length because of the effect of the polishing area. A large down force, high roll speed, high table feed rate, and high slurry flow rate were effective for reducing the NU. These results will be helpful for understanding the newly developed Roll-CMP process.